Exploring a deep, toothy mystery

There is much to learn about sharks, "one of the last frontiers,'' says zoology professor Phil Motta, who studies their feeding habits.

By LINDA GIBSON

© St. Petersburg Times, published May 5, 2000

TAMPA -- Phil Motta can tell you everything about shark bites except how they feel.

As a zoology professor at the University of South Florida, he commands a lab where every aspect of a shark's bite is recorded, measured and analyzed.

The closest he has come to personally experiencing a bite was when four gray reed sharks backed him into an underwater cave in the South Pacific. Arrayed before him outside the cave, they arched their backs and dropped their pectoral fins to convey an unmistakable message: We'd just as soon bite as back off. Give us an excuse.

Was he scared?

"Oh, definitely," Motta said. "They're very dangerous." Eventually, the sharks swam harmlessly away.

Motta has studied sharks for 20 years, concentrating on how they catch prey. Their anatomy is simple, but their feeding styles vary.

Some are ram feeders that simply overtake their prey. Filter feeders swim open-mouthed to catch whatever is out there, mostly plankton.

Suction feeders simply stay in one place and wait for the prey to swim to them, swiftly sucking down any fish careless enough to get too close.

"My kids do it with spaghetti," he said.

Then there's the difference between biting, in which just a piece of prey is taken, and gouging. To gouge a big chunk out of something like a sea lion, the shark detaches its upper jaw from its skull, giving his open mouth the look of a toothy cavern.

Despite the fascination with sharks, little is known about even their most basic behavior.

"Sharks are one of the last frontiers," Motta said.

He works at Mote Marine Laboratory in Sarasota with Dr. Robert Hueter to map out the basics of that frontier in terms of feeding behavior. Funded by a National Science Foundation grant, they have sharks flown in ("UPS, next day air delivery") and deposited in a holding tank there.

After anesthetizing a shark, Motta and Heuter thread 24 electrodes on a wire the diameter of a human hair into various muscles of the animal's head. It's delicate work. A fraction of an inch too far or not far enough, and they might hit a muscle that has nothing to do with feeding.

Then they wait for the anesthesia to wear off and the shark to begin swimming. A sacrificial fish is dropped into the tank as a food offering.

A high-speed camera shooting 1,000 frames per second records the action. The electrodes tell them which muscles are used to bite, tear, chew or swallow. These signals are run through amplifiers to a video player, then converted to digital information that ends up on a spreadsheet in Excel.

The result?

Motta can tell you that the total bite time of a Caribbean reef shark, a ram feeder, is 0.383 seconds, or less than half a second.

He's been studying sharks since his boyhood in Jamaica, where he started spear-fishing for them off the reefs at age 14. Now he guides students on shark-watching trips to the Bahamas, where tour-boat operators drop a diver into the water to feed the 20 or 30 sharks circling the boat.

Motta and his students watch from below, sitting underwater in a circle while the sharks mob the guy with the food.

"It's a little unnerving," he said.

But so far no tourist, scientist or graduate student has been bitten.

-- Linda Gibson can be reached at (813) 226-3382 or gibson@sptimes.com.

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